1) Field of the Invention
The present invention relates to a group signature system and an information processing apparatus for permitting a signature to be made by a member belonging to a group and making it possible to confirm the signature, a key issuing method for issuing a key at the time a new member is added to the group signature system, and a program for enabling a computer to carry out the key issuing method.
2) Description of the Related Art
Group signature systems of the background art are disclosed in “Jan Camenisch. Jens Groth. Group Signatures: Better Efficiency and New Theoretical Aspects. SCN 2004, vol. 3352 of LNCS. pp. 120-133, 2004” (hereinafter referred to as Non-patent document 1), and “Furukawa, Imai. An Efficient Group Signature Scheme from Bilinear Maps. ACISP 2005, vol. 3574 of LNCS, pp. 455-467” (hereinafter referred to as Non-patent document 2). In the group signature systems of the background art, a join protocol for adding a group member has the following structural features:
According to the join protocol of the group signature systems of the background art, a user apparatus first calculates data using a secret key. Then, the user apparatus sends the data to an issuer apparatus (referred to as group manager in Non-patent document 1 and membership manager in Non-patent document 2). Thereafter, the user apparatus proves the legitimacy of the data to the issuer apparatus. The issuer apparatus then processes the data using a secret key of the issuer apparatus.